Simple synthesis of benzoxazoles, benzimidazoles and benzothiazolesusing saccharin sulfonic acid as a proficient and reusable catalyst

Benzoxazoles, benzimidazoles and benzothiazoles are important class of compounds andhave exhibited a variety of pharmacological and biological activities such as melatoninreceptor agonist, anticancer, anti microbacterial, elastase inhibitory, photochromic agents andlaser dyes [۱]. There are several known strategies for the synthesis of these heterocycliccompounds includes: coupling of Carboxylic acids, acid chlorides, nitriles, aldeydes andorthoesters with ۲-substituted anilines, Beckmann rearrangement of ۲-acylphenol oximes andphotocyclization of phenolic Schiff bases [۲]. These methods often need long reaction timesand harsh conditions. These condensations usually are carried out by thermal fusion, heatingin solvents or in various concentrations of hydrochloric, sulfuric acid or polyphosphoric acid,or by heating under pressure in the presence of dilute hydrochloric acid [۳]. So, introduce of anew method for this conversion is necessary. In the recent years, Saccharin sulfonic acid(SaSA) has been used in organic transformations including trimethylsilylation of alcohols,acetylation of alcohols, phenols and amines, N-Boc protection of amines and formation of tbutylethers from alcohols, deprotection of ۱,۱-diacetates and preparation of ۱,۸-dioxooctahydroxanthenes and ۱۴-aryl-۱۴H-dibenzo[a,j]xanthenes [۴]. In continuation of ourinterest in the development of synthetic methods for the preparation of heterocycliccompounds we have focused our attention to the preparation of benzoxazoles, benzimidazolesand benzothiazoles by reaction between ۲-substituted anilines and nitriles in the presence ofsaccharin sulfonic acid as efficient acidic catalyst (Scheme ۱).

کلیدواژه ها:

saccharin sulfonic acid ، benzoxazole ، benzimidazole ، benzothiazole